Field of the Invention
The present invention relates to a static convertor plant for connection between a DC network and an AC network and comprising at least one convertor group, each group comprising at least two convertors having AC terminals for connection to the AC network and DC terminals for connection to the DC network.
The DC voltage U.sub.d of a convertor is obtained as a function of the control angle .alpha., the maximum DC voltage U.sub.dio and the direct current I.sub.d from the relationship EQU U.sub.d = U.sub.dio (cos.alpha. - d.sub.x1 I.sub.d /I.sub.d1)
where U.sub.dio is proportional to the amplitude of the AC voltage. d.sub.x1 is the relative DC voltage drop at rated DC, I.sub.d1. The convertor consumes a reactive power Q from the AC network, and Q is obtained from EQU Q = U.sub.dio I.sub.d .sqroot.1 - (U.sub.d /U.sub.dio).sup.2
A convertor frequently operates for the greater part of the time with a DC voltage which is considerably less than the maximum DC voltage, that is U.sub.d /U.sub.dio &lt;&lt; 1, so the reactive power Q increases rapidly with the load current I.sub.d. A result of this is that the comsumption of reactive power of the convertor will vary strongly with the load current, which, particularly in convertors for high power, may lead to serious drawbacks, for example strong voltage variations in the AC network.